Effects of Nitrogen Nutrition on Nitrogen Partitioning between Chloroplasts and Mitochondria in Pea and Wheat

Abstract

Nitrogen partitioning among proteins in chloroplasts and mitochondria was examined in pea (Pisum sativum L.) and wheat (Triticum aestivum L.) grown hydroponically with different nitrogen concentrations. In pea leaves, chloroplast nitrogen accounted for 75 to 80% of total leaf nitrogen. We routinely found that 8% of total ribulose-1,5-bisphosphate carboxylase/oxygenase adhered to thylakoids during preparation and could be removed with Triton X-100. With this precaution, the ratio of stroma nitrogen increased from 53 to 61% of total leaf nitrogen in response to the nitrogen supply, but thylakoid nitrogen remained almost constant around 20% of total. The changes in the activities of the stromal enzymes and electron transport in response to the nitrogen supply reflected the nitrogen partitioning into stroma and thylakoids. On the other hand, nitrogen partitioning into mitochondria was appreciably smaller than that in chloroplasts, and the ratio of nitrogen allocated to mitochondria decreased with increasing leaf-nitrogen content, ranging from 7 to 4% of total leaf nitrogen. The ratio of mitochondrial respiratory enzyme activities to leafnitrogen content also decreased with increasing leaf-nitrogen content. These differences in nitrogen partitioning between chloroplasts and mitochondria were reflected in differences in the rates of photosynthesis and dark respiration in wheat leaves measured with an open gas-exchange system. The response of photosynthesis to nitrogen supply was much greater than that of dark respiration, and the CO2 compensation point decreased with increasing leaf-nitrogen content.Nitrogen is the most important element for higher plants, and plant productivity is to a large extent determined by nitrogen nutrition. Photosynthesis and respiration are two major physiological processes in plants that determine plant productivity, but there are few studies of the balance between photosynthesis and respiration in relation to nitrogen nutrition. Much attention has been paid to the relationship between photosynthesis, nitrogen nutrition, and the role of Rubisco in nitrogen use efficiency (7,15,30 thylakoids (24). We have taken precautions against this problem. Nitrogen allocation to mitochondria has not been examined in previous studies, even though enzymes of photorespiratory decarboxylation are major protein components of these organelles (6, 10, 28). We anticipate that even though mitochondrial nitrogen is probably a quantitatively smaller component of total leaf nitrogen, it might be responsive to factors associated with photorespiratory activities, such as Rubisco amount and activity, and therefore to nitrogen nutrition and CO2 concentration.In this study, we grew pea and wheat hydroponically with different nitrogen concentrations at ambient CO, and examined the effects on the nitrogen distribution in chloroplasts and mitochondria. Several enzyme activities located in these organelles were also measured, and the results were related to observations of photosynthesis and respiration measured by...

Testing a Mechanistic Model of Forest-Canopy Mass and Energy Exchange Using Eddy Correlation: Carbon Dioxide and Ozone Uptake by a Mixed Oak-Maple Stand

“…Similarly, if Acer leaf V, (,,,) at the site was 30 ,urn01 C02 mV2 leaf s-I and N was 0.11 rnol N m-2 leaf, f N b would have been c. 0.066 with kt = unity. By comparison, f N b exceeded 0.3 for well fertilised Pisum sativum (Makino and Osmond 1991), and values in the range 0.15-0.30 may be common for other herbaceous plants (Evans 1989).…”

The respiratory energy requirements involved in nocturnal carbohydrate export from starch-storing mature source leaves and their contribution to leaf dark respiration

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Mobilization of Rubisco and Stroma-Localized Fluorescent Proteins of Chloroplasts to the Vacuole by anATGGene-Dependent Autophagic Process

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